Atrial fibrillation (also called “AF” or “A Fib”) is the most common abnormal heart rhythm. It is a very fast, uncontrolled heart rhythm caused when the upper changes of the heart (the atria) quiver instead of beating. During atrial fibrillation, the upper chambers of the heart beat between 350 and 600 times per minute, causing the pumping function of the upper chambers to not work properly. As a result, blood is not completely emptied from the heart's chambers, causing it to pool and sometimes clot. In about 5 percent of patients with atrial fibrillation, clotted blood dislodges from the atria and results in a stroke. The American Heart Association estimates that, in the United States, atrial fibrillation is responsible for over 70,000 strokes each year.
Various methods exist for treating atrial fibrillation. One such method is cardiac ablation, which is a medical procedure performed to prevent abnormal electrical impulses from ever beginning in the first place. In an ablation procedure, the electrophysiologist first pinpoints the precise area in the heart at which the abnormal signals start through a mapping procedure. The electrophysiologist then eliminates the small area of tissue that is causing the arrhythmia by ablating that tissue. With a procedure known as AV nodal ablation, the electrophysiologist ablates the AV node, keeping the abnormal impulses from traveling to the heart's lower chambers. A pacemaker is used to regulate the heartbeat after this therapy.
Another method for treating atrial fibrillation is AF suppression. With this method, an implanted pacemaker stimulates the heart in a way that preempts any irregular rhythms.
In about half of the atrial fibrillation cases, medication can be effective in controlling the rate at which the upper and lower chambers of the heart beat. Standard medications used for atrial fibrillation include beta-blockers (such as carvedilol and propanolol) and calcium-channel clockers (like verapamil and diltiazem), which slow the heart rate. Digoxin, which slows the heart rate through the AV node, thereby decreasing the rate at which the electrical impulses conduct from the upper to lower chambers, can also be used. Other medications, such as disopyramide, flecainide, procainamide and sotalol, are used to chemically convert AF back to normal rhythm. In many cases, anticoagulants, such as heparin, are also used to “thin” the blood to reduce the risk of clot formation.
Cardioversion can also be used to treat atrial fibrillation. Cardioversion involves changing an abnormal heart rate back to a normal one. Cardioversion can be done using medication or electricity. In electrical cardioversion, energy is applied to the heart to “jolt” it out of atrial fibrillation. Two types of electrical cardioversion exist, external and internal. For external cardioversion, two external paddles are placed on the patient's chest or on the chest and back. A high-energy electrical shock is sent through the patches and through the body to the heart. The energy shocks the heart out of atrial fibrillation and back into normal rhythm.
Internal cardioversion uses a similar approach, but instead of paddles being placed on the outside of the body, a catheter is inserted through a vein to the heart. The electrical energy is delivered through the catheter to the inside of the heart to stop the atrial fibrillation. Internal cardioversion has met with high success and provides a desirable alternative to external cardioversion. Notably, internal cardioversion requires far lower energy levels than external cardioversion and thus can provide a more comfortable procedure for patients by eliminating the trauma, discomfort and risk associated with high-energy external cardioversion.
Electrophysiologists are developing clinical techniques targeted toward the use of catheter-based ablation as a therapeutic alternative in the treatment of focally induced atrial fibrillation. An important component of these efforts are methods for quickly and reliably inducing and converting the AF arrhythmia while the patient is in the electrophysiology lab.